A cloud service is available, and various database services are providable through the Internet. In other words, an information provider may store various types of data in a database server provided by a cloud service provider and provide a database service. In this case, it is unnecessary for the information provider to manage the database server, and borrows the database server managed by the cloud service provider.
In provision of such a database service, since the cloud service provider different from the information provider manages the database server, there is a possibility that risk of data leakage may increase. For example, the cloud service provider may directly access the data stored in the provided database server, and the information provider may hesitate to provide valuable data. In addition, even for a user of the database service, the cloud service provider and the information provider may be aware of what kind of query was issued to a database. For this reason, since there is a possibility that intention of the user of the database service will be presumed by another person, the user may hesitate to use the database service.
A concealment calculation technology that allows query management in a state in which both or one of a query and data stored in a database server is encrypted has been proposed to solve the above-mentioned problem (for example, see Patent Literatures 1 to 9).